Reasoning and Evidence

This chapter links the principles of reasoning and evidence to the larger tasks of preparing a persuasive case and of evaluating a persuasive case. Syllogisms are forms of reasoning that begin with a major premise, add a minor premise, and arrive at a conclusion. Enthymemes suppress one or more of the parts of the syllogism, leaving it for the audience to fill in themselves. Propositions are debatable assertions, of which three types are generally recognized: policy, fact, and value. Stock issues could be defined as systematized common sense. The believability of factual claims rests on evidence and on inferences drawn from that evidence. Evidence can also be brought to bear on value issues. A fallacious argument is one that fails to stand up to careful scrutiny. Persuasion typically takes place under conditions that are less than ideal for reflective argumentative exchange. Under the circumstances, persuaders cannot be expected to win belief by logic alone.